Determination of the acid dissociation constants of the p-sulphonato-calix[4]arene


1 Department of Chemistry, Islamic Azad University, Science and Research Branch, Tehran, Iran

2 Department of Chemistry, Faculty of Science and Engineering, Islamic Azad University, Saveh Branch, Saveh, Iran


The acid dissociation constants of the hydroxyl groups in 25, 26, 27, 28-tetrahydroxy-5, 11, 17, 23-tetrasulphonic-calix[4]arene (SC4) were determined at 25οC by a combination of potentiometric and spectrophotometric titration method. The first and second acid dissociation constants (pKa1, pKa2) were found to be 3.19 and 12.1, which demonstrated pKa shift due to intramolecular hydrogen bonding interactions among hydroxyl groups in SC4.